Method to reduce program disturbs in non-volatile memory cells

ABSTRACT

A non-volatile memory and methods of operating the same to reduce disturbs is provided. In one embodiment, the method includes coupling a first positive high voltage to a first global wordline in a first row of an array of memory cells, and coupling a second negative high voltage (V NEG ) to a first bitline in a first column of the array to apply a bias to a non-volatile memory transistor in a selected memory cell to program the selected memory cell. A margin voltage having a magnitude less than VNEG is coupled to a second global wordline in a second row of the array, and an inhibit voltage coupled to a second bitline in a second column of the array to reduce a bias applied to a non-volatile memory transistor in an unselected memory cell to reduce program disturb of data programmed in the unselected memory cell due to programming.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/664,131 , filed Mar. 20, 2015 , now U.S. Pat. No. 9,431,124 , IssuedAug. 30, 2016 , which is a continuation of U.S. patent application Ser.No. 14/216,589 , filed Mar. 17, 2014 , Now U.S. Pat. No. 8,988,938 ,Issued on Mar. 24, 2015 , which is a continuation of U.S. patentapplication Ser. No. 13/920,352 , filed Jun. 18, 2013 , now U.S. Pat.No. 8,675,405 , issued Mar. 18, 2014 , which claims the benefit ofpriority to U.S. Provisional Patent Application No. 61/778,136 , filedMar. 12, 2013 , all of which are incorporated by reference herein intheir entirety.

TECHNICAL FIELD

The present disclosure relates generally to memory devices, and moreparticularly to methods for reducing program disturbs in non-volatilememory cells.

BACKGROUND

Non-volatile memories are widely used for storing data in computersystems, and typically include a memory array with a large number ofmemory cells arranged in rows and columns. Each of the memory cellsincludes a non-volatile charge trapping gate field-effect transistorthat is programmed or erased by applying a voltage of the properpolarity, magnitude and duration between a control gate and thesubstrate. A positive gate-to-substrate voltage causes electrons totunnel from the channel to a charge-trapping dielectric layer raising athreshold voltage (V_(T)) of the transistor, and a negativegate-to-channel voltage causes holes to tunnel from the channel to thecharge-trapping dielectric layer lowering the threshold voltage.

Non-volatile memories suffer from program or bitline disturbs, which isan unintended and detrimental change in memory cell V_(T) when anothermemory cell connected to the same bitline is inhibited from beingprogrammed. Bitline disturb refers to disturb of the memory cellslocated in a row different from the row containing the cell undergoingprogramming. Bitline disturb occurring in the deselected row increasesas the number of erase/program cycles in rows selected in the commonwell increases. The magnitude of bitline disturb also increases athigher temperatures, and, since memory cell dimensions scale down fasterthan applied voltages at advanced technology nodes, bitline disturb alsobecomes worse as the density of non-volatile memories increase.

It is, therefore, an object of the present invention to provide improvednon-volatile memories and methods of programming the same.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detaileddescription that follows and from the accompanying drawings and theappended claims provided below, where:

FIG. 1 is a block diagram illustrating a cross-sectional side view of anon-volatile memory transistor or device;

FIG. 2 is a schematic diagram illustrating a two transistor (2T) memorycell for which an embodiment of the present disclosure is particularlyuseful;

FIG. 3 is a schematic diagram is a segment of a memory arrayillustrating an embodiment of a program operation according to thepresent disclosure;

FIG. 4 is a graph illustrating a positive high voltage (V_(POS)), anegative high voltage (V_(NEG)), and an intermediate, margin voltage(V_(MARG)) according to an embodiment of the present disclosure;

FIG. 5 is a graph illustrating voltages applied to a selected globalwordline (V_(SELECTED WL)) and a deselected global wordline(V_(DESELECTED GWL)) during a program operation according to anembodiment of the present disclosure;

FIG. 6 is a block diagram illustrating a processing system including amemory device according to an embodiment of the present disclosure;

FIGS. 7A-7C are block diagrams illustrating details of command andcontrol circuitry of a non-volatile memory according to variousembodiments of the present disclosure; and

FIG. 8 is a flowchart illustrating a method for reducing bitlinedisturbs in unselected memory cells according to an embodiment of thepresent disclosure.

DETAILED DESCRIPTION

Methods for reducing program disturbs in non-volatile memories aredescribed herein. The method is particularly useful for operatingmemories made of memory arrays of bit cells or memory cells includingnon-volatile trapped-charge semiconductor devices that may be programmedor erased by applying a voltage of the proper polarity, magnitude andduration.

In the following description, for purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. It will be evident, however, toone skilled in the art that the present invention may be practicedwithout these specific details. In other instances, well-knownstructures, and techniques are not shown in detail or are shown in blockdiagram form in order to avoid unnecessarily obscuring an understandingof this description.

Reference in the description to “one embodiment” or “an embodiment”means that a particular feature, structure, or characteristic describedin connection with the embodiment is included in at least one embodimentof the invention. The appearances of the phrase “in one embodiment” invarious places in the specification do not necessarily all refer to thesame embodiment. The term to couple as used herein may include both todirectly electrically connect two or more components or elements and toindirectly connect through one or more intervening components.

The non-volatile memory may include memory cells with a non-volatilememory transistor or device implemented usingSilicon-Oxide-Nitride-Oxide-Silicon (SONOS) or floating gate technology.

In one embodiment, illustrated in FIG. 1, the non-volatile memorytransistor or device is a SONOS-type non-volatile memory device.Referring to FIG. 1, a SONOS device 100 includes a gate stack 102 formedover a substrate 104. The SONOS device 100 further includes source/drainregions 106 formed in a well 108 in the substrate 104 on either side ofgate stack 102, which define a channel region 110 underneath gate stack.Gate stack 102 includes an oxide tunnel dielectric layer 112, a nitrideor oxynitride charge-trapping layer 114, a top, blocking oxide layer 116and a poly-silicon (poly) or metal layer which serves as a control gate118.

When the control gate 118 is appropriately biased, electrons from thesource/drain regions 106 are injected or tunnel through tunneldielectric layer 112 and are trapped in the charge-trapping layer 114.The mechanisms by which charge is injected can include bothFowler-Nordheim (FN) tunneling and hot-carrier injection. The chargetrapped in the charge-trapping layer 114 results in an energy barrierbetween the drain and the source, raising the threshold voltage V_(T)necessary to turn on the SONOS device 100 putting the device in a“programmed” state. The SONOS device 100 can be “erased” or the trappedcharge removed and replaced with holes by applying an opposite bias onthe control gate 118.

In another embodiment, the non-volatile trapped-charge semiconductordevice can be a floating-gate MOS field-effect transistor (FGMOS) ordevice. Generally, is similar in structure to the SONOS device 100described above, differing primarily in that a FGMOS includes apoly-silicon (poly) floating gate, which is capacitively coupled toinputs of the device, rather than a nitride or oxynitridecharge-trapping. Thus, the FGMOS device can be described with referenceto FIG. 1. Referring to FIG. 1, a FGMOS device 100 includes a gate stack102 formed over a substrate 104. The FGMOS device 100 further includessource/drain regions 106 formed in a well 108 in the substrate 104 oneither side of gate stack 102, which define a channel region 110underneath gate stack. Gate stack 102 includes a tunnel dielectric layer112, a floating gate layer 114, a blocking oxide or top dielectric layer116 and a poly-silicon or metal layer which serves as a control gate118.

Similarly to the SONOS device described above the FGMOS device 100 canbe programmed by applying an appropriate bias between the control gateand the source and drain regions to inject charge in to thecharge-trapping layer, raising the threshold voltage V_(T) necessary toturn on the FGMOS device. The FGMOS device can be erased or the trappedcharge removed by applying an opposite bias on the control gate.

A memory array is constructed by fabricating a grid of memory cellsarranged in rows and columns and connected by a number of horizontal andvertical control lines to peripheral circuitry such as address decodersand sense amplifiers. Each memory cell includes at least onenon-volatile trapped-charge semiconductor device, such as thosedescribed above, and may have a one transistor (1T) or two transistor(2T) architecture.

In one embodiment, illustrated in FIG. 2, the memory cell 200 has a2T-architecture and includes, in addition to a non-volatile memorytransistor 202, a pass or select transistor 204, for example, aconventional IGFET sharing a common substrate connection 206 with thememory transistor 202. Referring to FIG. 2, the memory transistor 202has a charge trapping layer 208 and a drain 210 connected to a source222 of the select transistor 204 and through the select transistor to abitline 212, a control gate 214 connected to a wordline 216 and a source218 connected to a source line 224. Select transistor 204 also includesa drain 220 connected to a bitline 212 and a gate 226 connected to aselect or read line 228.

During an erase operation to erase the memory cell 200 a negative highvoltage (V_(NEG)) is applied to the wordline 216 and a positive highvoltage (V_(POS)) applied to the bitline and the substrate connection206. Generally, the memory cell 200 is erased as part of a bulk eraseoperation in which all memory cells in a selected row of a memory arrayare erased at once prior to a program operation to program the memorycell 200 by applying the appropriate voltages to a global wordline (GWL)shared by all memory cells in the row, the substrate connection and toall bitlines in the memory array.

During the program operation the voltages applied to the wordline 216and the bitline 212 are reversed, with V_(POS) applied to the wordlineand V_(NEG) applied to the bitline, to apply a bias to program thememory transistor 202. The substrate connection 206 or connection to thewell in which the memory transistor 202 is formed is coupled toelectrical ground, V_(NEG) or to a voltage between ground and V_(NEG).The read or select line 228 is likewise coupled to electrical ground(0V), and the source line 224 may be at equipotential with the bitline212, i.e., coupled to V_(NEG), or allowed to float.

After an erase operation or program operation is completed, the state ofthe memory cell 200 can be read by setting a gate-to-source voltage(V_(GS)) of the memory transistor 202 to zero, applying a small voltagebetween the drain terminal 210 and source terminal 218, and sensing acurrent that flows through the memory transistor. In the programmedstate, an N-type SONOS memory transistor, for example, will be OFFbecause V_(GS) will be below the programmed threshold voltage V_(TP). Inthe erased state, the N-type memory transistor will be ON because theV_(GS) will be above an erased threshold voltage V. Conventionally, theON state is associated with a logical “0” and the OFF state isassociated with a logical “1.”

A memory array of memory cells and methods of operating the same toreduce disturbs will now be described with reference to FIG. 3 and TableI below. In the following description, for clarity and ease ofexplanation, it is assumed that all of the transistors in memory arrayare N-type SONOS transistors. It should be appreciated, without loss ofgenerality that a P-type configuration can be described by reversing thepolarity of the applied voltages, and that such a configuration iswithin the contemplated embodiments of the invention. In addition, thevoltages used in the following description are selected for ease ofexplanation and represent only one exemplary embodiment of theinvention. Other voltages may be employed in different embodiments ofthe invention.

FIG. 3 illustrates an exemplary embodiment of a segment of a memoryarray 300, which may be part of a large memory array of memory cells. InFIG. 3, memory array 300 includes four memory cells 301, 302, 303 and304 arranged in two rows (ROW 1, ROW 2) and two columns (COLUMN 1,COLUMN 2). Each of the memory cells 301-304 may be structurallyequivalent to memory cell 200 described above.

Referring to FIG. 3, memory cell 301 is the targeted cell to beprogrammed to a logic “1” state (i.e., programmed to an ON state) whilememory cell 302, already erased to a logic “0” state by a precedingerase operation, is maintained in a logic “0” or OFF state. These twoobjectives (programming cell 301 and inhibiting cell 302) areaccomplished by applying a first or positive high voltage (V_(POS)) to afirst global wordline (GWL₁) in the first row of the memory array 300, asecond or negative high voltage (V_(NEG)), is applied to a first bitline(BL₁) to bias transistor T1 on programming the selected memory cell 301,while an inhibit voltage (V_(Inhib)) is applied to a second bitline(BL₂) to bias transistor T2 off on inhibiting programming of thedeselected memory cell 302, and a common or shared voltage is applied tothe substrate nodes (SUB) of all memory cells 301, 302, 303 and 304, andthe read lines (RL1 and RL2) coupled to electrical ground (0V). Thesource lines (SL1 and SL2) may be at equipotential with the bitlines intheir respective columns, i.e., SL1 is coupled to V_(NEG) and SL2coupled to the V_(Inhib), or allowed to float.

In addition, and as described in greater detail below, a selected marginvoltage (V_(MARG)) having a voltage level or magnitude less than V_(NEG)is applied to a second global wordline (GWL₂) in the second row of thememory array 300 to reduce or substantially eliminate program-statebitline disturb in the deselected memory cell 304 due to programming ofthe selected memory cell 301.

Table I depicts exemplary bias voltages that may be used for programminga non-volatile memory having a 2T-architecture and including memorycells with N-type SONOS transistors.

TABLE I Substrate GWL1 BL1 SL1 RL1 Node GWL2 BL2 SL2 RL2 V_(POS) +4.7 VV_(NEG) −3.6 V Float/−3.6 V V_(GND) 0.0 V V_(NEG) −3.6 V V_(Marg) −2.6 VV_(Inhib) +1.2 V Float/+1.2 V V_(GND) 0.0 V

Because the voltage applied to the second global wordline (GWL2) has alower voltage level or magnitude that V_(NEG), which is conventionallyapplied to wordlines in deselected row or cells, the gate to drainvoltage (V_(GD)) across transistor T4 is 3.8V, as compared to a V_(GD)in conventionally operated memories of 4.8V, the amount of bitlinedisturb of the threshold V_(T) of T4 is reduced significantly. In oneembodiment of this invention it was observed to be reduced from about 60mV to less than about 7 mV.

The margin voltage (V_(MARG)) can be generated using dedicated circuitryin the memory (not shown in this figure) used solely for generatingV_(MARG), or can be generated using circuitry already included in thememory device. Generally, the margin voltage (V_(MARG)) has the samepolarity as the second or V_(NEG) high voltage, but is higher or morepositive than V_(NEG) by a voltage equal to at least the thresholdvoltage (V_(T)) of the transistor T4 in the memory cell 304 for whichprogram state bitline disturb is reduced. Optionally, the circuitry usedto generate the margin voltage (V_(MARG)) is programmable to set adesired margin voltage (V_(MARG)) with steps, in one embodiment, of 14mV or less.

In one embodiment, the circuitry used to generate the margin voltage(V_(MARG)) includes a digital-to-analog-converter (DAC) enabled bycommand and control circuitry in the memory programmed to generate amargin voltage (V_(MARG)) of a desired magnitude or voltage level to becoupled to the GWLs of deselected row(s) during the program operation.In one particular advantageous embodiment the DAC is a margin mode DACin the memory, which is used during initialization of the memory toadjust voltages therein, and which is not normally enabled during theprogram operation. Significant advantages of this embodiment includethat V_(MARG) can be trimmed using the (MDAC) bits, it does notrepresent a large load on a negative pump for V_(NEG) and an outputbuffer of the margin mode DAC offers a low impedance driver for theV_(MARG) signal. Adapting such a margin mode DAC for generating V_(MARG)during the program operation requires forming an electrical connectionto the GWLs of deselected rows of the memory array 300 during theprogram operation, and enabling the margin mode DAC through a DAC enablesignal.

In certain embodiments, further adaption of the V_(MARG) circuit isdesirable to overcome the fact that V_(MARG) was not originally designedto drive large capacitive loads active during program. One method ofovercoming this limitation will now be described with reference to thegraphs of FIGS. 4 and 5.

FIG. 4 is a graph illustrating a positive first high voltage (V_(POS)402), a negative second high voltage (V_(NEG) 404), and an intermediate,margin voltage (V_(MARG) 406) according to an embodiment of the presentdisclosure. Referring to FIG. 4 it is noted that the start-up time forthe circuit generating the margin voltage (V_(MARG) 406) can berelatively slow, up to 80-110 μs, as compared to the second high voltage(V_(NEG) 404). During this time the voltage difference between adeselected global wordline (GWL₂) to which the margin voltage (V_(MARG)406) is applied and the p-well (SPW) or substrate node to which secondhigh voltage (V_(NEG) 404), can reach 1.6-1.7 volts for 20-40 μs. Thus,to reduce erase-state bitline disturb in an unselected memory cell inthe first column and second row of the memory array (e.g., cell T3),V_(NEG) is coupled to the second global wordline (GWL₂) in thedeselected row for up to about 40 μs until a capacitance associated withthe deselected wordline(s) is sufficiently pre-charged, and V_(NEG) hasreached a value close to −2.0 volts. The margin voltage is then coupledto the global wordline (GWL₂) in the deselected row for the remainder ofthe program operation to reduce program-state bitline disturb in asecond unselected memory cell in the second column and second row of thememory array due to programming of the selected memory cell.

A graph illustrating voltages applied to a selected global wordline(V_(SELECTED WL) 502) and a deselected global wordline(V_(DESELECTED GWL) 504) during a program operation according to anembodiment of the present disclosure is shown in FIG. 5. Referring toFIG. 5 it is noted from the graph of the deselected global wordlinevoltage (V_(DESELECTED GWL) 504) that at about 15 μs, indicated byreference numeral 506 on the graph of the deselected global wordlinevoltage, the global wordline (GWL₂) in the deselected row is switchedfrom being coupled to second high voltage (V_(NEG) 404), to beingcoupled to the margin voltage (V_(MARG) 406) for the remainder of theprogram operation.

A processing system 600 to reduce bitline program disturbs according toan embodiment of the present disclosure will now be described withreference to FIG. 6.

Referring to FIG. 6 the processing system 600 generally includes anon-volatile memory 602 coupled to a processor 604 in a conventionalmanner via an address bus 606, a data bus 608 and a control bus 610. Itwill be appreciated by those skilled in the art that the processingsystem of FIG. 6 has been simplified for the purpose of illustrating thepresent invention and is not intended to be a complete description. Inparticular, details of the processor, row and column decoders, senseamplifiers and command and control circuitry, which are known in the arthave are not described in detail herein.

The processor 604 may be a type of general purpose or special purposeprocessing device. For example, in one embodiment the processor can be aprocessor in a programmable system or controller that further includes anon-volatile memory, such as a Programmable System On a Chip or PSoC™controller, commercially available from Cypress Semiconductor of SanJose, Calif.

The non-volatile memory 602 includes a memory array 612 organized asrows and columns of non-volatile memory cells (not shown in this figure)as described above. The memory array 612 is coupled to a row decoder 614via multiple wordlines and read lines 616 (at least one wordline and oneread line for each row of the memory array) as described above. Thememory array 612 is further coupled to a column decoder 618 via amultiple bitlines and source lines 620 (one each for each column of thememory array) as described above. The memory array 612 is coupled to aplurality of sense amplifiers 622 to read multi-bit words therefrom. Thenon-volatile memory 602 further includes command and control circuitry624 to control the row decoder 614, the column decoder 618 and senseamplifiers 622, and to receive read data from sense amplifiers. Thecommand and control circuitry 624 includes voltage control circuitry 626to generate the voltages needed for operation of the non-volatile memory602, including V_(POS), V_(NEG) and V_(INHIB), and a margin mode DAC 628to generate V_(MARG) described above, which is routed through thevoltage control circuitry to the row decoder 614. The voltage controlcircuitry 626 operates to apply appropriate voltages to the memory cellsduring read, erase and program operations.

The command and control circuitry 624 is configured to control the rowdecoder 614 to select a first row of the memory array 612 for a programoperation by applying a V_(POS) to a first global wordline (GWL₁) in thefirst row and to deselect a second row of the memory array by applying amargin voltage to a second global wordline (GWL₂) in the second row. Insome embodiments, the command and control circuitry 624 is configured tosequentially couple first V_(NEG) to the second global wordline for abrief period of time and then the margin voltage. As described above, insome embodiments, the start-up time for a margin voltage circuit can berelatively slow as compared to that of V_(NEG) coupled to a substratenode or p-well (SPW) in which the memory transistor is formed, andduring this time the voltage bias difference between the deselectedwordline (GWL₂) and a p-well (SPW) or substrate node can causeerase-state bitline disturb in an unselected memory cell in the firstcolumn and second row of the memory array (e.g., cell T3). Thus, toreduce erase-state bitline disturb in the unselected memory cell in thefirst column and second row of the memory array (e.g., cell T3), V_(NEG)is coupled to the second global wordline (GWL₂) in the deselected rowfor a brief time until a capacitance associated with the deselectedwordline(s) is sufficiently pre-charged, and V_(NEG) has reached a valueclose to −2.0 volts. The margin voltage is then coupled to the globalwordline (GWL₂) in the deselected row for the remainder of the programoperation to reduce program-state bitline disturb in a second unselectedmemory cell in the second column and second row of the memory array dueto programming of the selected memory cell.

The command and control circuitry 624 is further configured to controlthe column decoder 618 to select a memory cell in the first row (e.g.,cell T1) for programming by applying a V_(NEG) to a first shared bitline(BL₁) in a first column, and to inhibit a unselected memory cell in thefirst row (e.g., cell T2) from programming by applying an inhibitvoltage to a second shared bitline (BL₂) in a second column. The columndecoder 618 may be further configured to apply V_(NEG) to a first sharedsource line (SL₁) in the first column, and to apply the inhibit voltageon a second shared source line (SL₂) in the second column.

Details of the command and control circuitry of a memory deviceaccording to various embodiments of the present disclosure will now bedescribed with reference to FIGS. 7A-7C.

Referring to FIG. 7A, in one embodiment the command and controlcircuitry 700 includes a negative HV supply or pump 702 to generate aV_(NEG) coupled to the bitline and source line of the selected cell, andto the substrate nodes during the program operation, adigital-to-analog-converter (DAC 704) enabled by the command and controlcircuitry to generate a margin voltage to be coupled to the GWLs ofdeselected rows during the program operation, and a switching circuit706 to switch between V_(NEG) and the margin voltage coupled to thedeselected GWLs during the program operation. The DAC 704 can be adedicated DAC used solely for generating V_(MARG), or a DAC alreadyincluded in the command and control circuitry 700 or voltage controlcircuitry 626 for other purposes, and which is normally not utilizedduring a program operation. As noted above, in one particularadvantageous embodiment the DAC is a margin mode DAC 628 in the commandand control circuitry 624 of the non-volatile memory 602, which is usedduring test to measure the threshold voltages of the non-volatiledevices therein, and which is not normally enabled during the programoperation. It will be appreciated that adapting such a margin mode DACfor generating V_(MARG) during the program operation requires forming anelectrical connection to the switching circuit 706, and through theswitching circuit and the row decoder (not shown in this figure) to theGWLs of deselected rows of the memory array during the programoperation. The command and control circuitry 624 of the non-volatilememory 602 enables the DAC 704 through a DAC enable signal, and,optionally, operates the DAC to provide a programmed margin voltagelevel or magnitude. Generally, the DAC 704 is operated to provide amargin voltage having a magnitude less than the voltage magnitude ofV_(NEG), i.e., higher or more positive than V_(NEG) in the N-type SONOSembodiment described above, by a voltage equal to at least the thresholdvoltage (V_(T)) of the of the memory transistor in the memory cell. Inother embodiments, the DAC 704 may be programmed or operated to providea margin voltage magnitude less than V_(NEG) by an amount close to theV_(T) of the memory transistor. For example, in one embodiment describedabove the DAC 704 may be programmed or operated to provide a marginvoltage adjustable to within one or more small steps of about 14 mVeach.

In another embodiment, shown in FIG. 7B, the command and controlcircuitry 700 includes a second charge pump 708 to generate the marginvoltage to be coupled to the GWLs of deselected rows during the programoperation. By selecting the second charge pump 708 to have a start-uptime and power to charge the capacitance associated with the deselectedwordline(s) that are substantially the same as the negative pump 702,the GWLs of the deselected rows can be coupled to the margin voltagethroughout the program operation, and thus the need for a separateswitching circuit 706 is eliminated.

In yet another embodiment, shown in FIG. 7C, the command and controlcircuitry 700 includes a voltage divider 710 coupled to an output ofnegative pump 702 to generate the margin voltage to be coupled to theGWLs of deselected rows during the program operation. Because V_(NEG)and V_(MARG) are both supplied by the negative pump 702 there issubstantially no difference in start-up time between V_(NEG) andV_(MARG), and the voltage bias difference between V_(MARG) applied thedeselected wordline (GWL₂) and V_(NEG) applied to the p-well (SPW) orsubstrate node cannot reach a voltage level sufficient to causeerase-state bitline disturb in the unselected memory cell in the firstcolumn and second row of the memory array (e.g., 1.6-1.7 volts for 20-40μs), the GWLs of the deselected rows can be coupled to the marginvoltage throughout the program operation, and thus the need for aseparate switching circuit 706 is eliminated.

FIG. 8 is a flowchart illustrating a method for reducing program disturbin one embodiment. Note, it will be understood that although all stepsof the method are described individually below implying a sequentialorder that is not necessarily the case, and that as shown in FIG. 8, afirst five individual steps of the method are performed at substantiallythe same time, while a last two steps are performed in order after onlya slight delay.

Referring to FIG. 8, a first positive high voltage (V_(POS)) is coupledto a first global wordline in a first row of a memory array of memorycells (802). In the next operation, a V_(NEG) is coupled to a firstshared bitline in a first column of the memory array to apply a bias toa non-volatile memory transistor in a selected memory cell to programthe selected memory cell (804). In embodiments in which the memorytransistors are formed in wells in a substrate, the wells may be coupledto electrical ground, a voltage between ground and V_(NEG), or, as inthe embodiment shown to V_(NEG) (806). Optionally, V_(NEG) may becoupled to a second global wordline in a second row of the memory arrayfor a brief period of time to apply a bias to a non-volatile memorytransistor in a first unselected memory cell in the first column and thesecond row of the memory array sharing the first shared bitline with theselected memory cell to reduce erase-state bitline disturb in the firstunselected memory cell (808). Simultaneously, a margin voltage less thanV_(NEG) is generated (810). In the next operation, after only a slightdelay the margin voltage is coupled to the second global wordline in thesecond row of the memory array (812). In the next operation, an inhibitvoltage is coupled to a second shared bitline in a second column of thememory array to apply a bias to a non-volatile memory transistor in asecond unselected memory cell in the second row and second column toreduce program-state bitline disturb in the second unselected memorycell (814).

Thus, embodiments of a non-volatile memory and methods of operating thesame to reduce disturbs have been described. Although the presentdisclosure has been described with reference to specific exemplaryembodiments, it will be evident that various modifications and changesmay be made to these embodiments without departing from the broaderspirit and scope of the disclosure. Accordingly, the specification anddrawings are to be regarded in an illustrative rather than a restrictivesense.

The Abstract of the Disclosure is provided to comply with 37 C.F.R.§1.72(b), requiring an abstract that will allow the reader to quicklyascertain the nature of one or more embodiments of the technicaldisclosure. It is submitted with the understanding that it will not beused to interpret or limit the scope or meaning of the claims. Inaddition, in the foregoing Detailed Description, it can be seen thatvarious features are grouped together in a single embodiment for thepurpose of streamlining the disclosure. This method of disclosure is notto be interpreted as reflecting an intention that the claimedembodiments require more features than are expressly recited in eachclaim. Rather, as the following claims reflect, inventive subject matterlies in less than all features of a single disclosed embodiment. Thus,the following claims are hereby incorporated into the DetailedDescription, with each claim standing on its own as a separateembodiment.

Reference in the description to one embodiment or an embodiment meansthat a particular feature, structure, or characteristic described inconnection with the embodiment is included in at least one embodiment ofthe circuit or method. The appearances of the phrase one embodiment invarious places in the specification do not necessarily all refer to thesame embodiment.

What is claimed is:
 1. A circuit, comprising: a memory array including,a plurality of memory cells, each comprising at least a non-volatilememory (NVM) transistor, arranged in rows and columns, wherein gates ofthe NVM transistors of memory cells in a same row couple to and share aglobal wordline; and a programmable control circuitry coupled to thememory array, wherein the programmable control circuitry includes avoltage control circuitry configured to provide, a first voltage to afirst global wordline in a first row of the memory array, and a secondvoltage to source-drain paths of memory cells in a first column of thememory array to apply a first bias voltage to the NVM transistor in aselected memory cell to program the selected memory cell, and a thirdvoltage to source-drain paths of memory cells in a second column of thememory array.
 2. The circuit of claim 1, wherein each of the pluralityof memory cells further includes a first end and a second end, whereinthe second ends of memory cells in a same column are coupled to andshare a bitline.
 3. The circuit of claim 2, wherein the first and secondvoltages are high voltages and the third voltage is an inhibit voltage(V_(INHIB)).
 4. The circuit of claim 2, wherein the second voltage isprovided to the source-drain paths of the memory cells in the firstcolumn of the memory array via a first bitline.
 5. The circuit of claim3, wherein the V_(INHIB) is provided to the source-drain paths of thememory cells in the second column of the memory array via a secondbitline, wherein the first bitline is different from the second bitline.6. The circuit of claim 1, wherein at least one of the plurality ofmemory cells of the memory array further comprises an insulated-gatefield-effect transistor (IGFET) coupled to the NVM transistor in series,wherein a source of the NVM transistor is coupled to the first end and adrain of the IGFET is coupled to the second end of the at least one ofthe plurality of memory cells, wherein gates of the IGFET in memorycells of the same row are coupled to and share a global read line. 7.The circuit of claim 1, wherein the first voltage and the second voltagehave opposite polarities, and the first voltage includes a magnitudethat is greater than the second voltage.
 8. The circuit of claim 1,wherein the NVM transistors of the plurality of memory cells aren-channel NVM transistors, and wherein the first voltage and the thirdare positive voltages and the second voltage is a negative voltage. 9.The circuit of claim 1, wherein the programmable control circuitry ofclaim 1 further comprises: a programmable digital-to-analog converter(DAC) configured to provide a margin voltage to a second global wordlinein a second row of the memory array, wherein the margin voltage includesa magnitude less than the second voltage by at least a threshold voltage(VT) of the NVM transistor in the unselected memory cell.
 10. Thecircuit of claim 1, wherein the first ends of the plurality of memorycells are configured to be coupled to a floating voltage.
 11. A methodof operating a memory circuit, comprising: coupling a positive voltageto a first global wordline in a first row of a memory array of memorycells and coupling a negative voltage to first ends of source-drainpaths of memory cells in a first column of the memory array to apply afirst bias voltage to a non-volatile memory transistor in a selectedmemory cell to program the selected memory cell; and coupling a voltagehaving a magnitude less than the negative voltage to a second globalwordline in a second row of the memory array and coupling an inhibitvoltage to first ends of source-drain paths of memory cells in a secondcolumn of the memory array.
 12. The method of claim 11, wherein theinhibit voltage is configured to minimize a second bias voltage appliedto a non-volatile memory transistor in an unselected memory cell due tothe programming of the selected memory cell.
 13. The method of claim 11,wherein the magnitude of the voltage coupled to the second globalwordline is less than the negative voltage by an amount at leastcorresponding to a threshold voltage of a transistor associated with theunselected memory cell.
 14. The method of claim 11, further comprising:generating, by a digital-to-analog converter (DAC), the voltage havingthe magnitude less than the negative voltage.
 15. The method of claim11, further comprising: at a first time, coupling the negative voltageto the second global wordline in the second row of the memory array,wherein the voltage having a magnitude less than the negative voltage iscoupled to the second global wordline at a second time.
 16. The methodof claim 11, wherein the negative voltage is applied to the source-drainpaths of the memory cells in the first column of the memory array via afirst bitline, and wherein the inhibit voltage is applied to thesource-drain paths of the memory cells in the second column of thememory array via a second bitline.
 17. The method of claim 15, furthercomprising: selecting the first row of the memory array for programming,using a row decoder, by applying the positive voltage to the firstglobal wordline; deselecting the second row of the memory array forprogramming, using the row decoder, by applying the voltage having themagnitude less than the negative voltage to the second global wordline;and selecting the selected memory cell in the first row for programming,using a column decoder, by applying the negative voltage to the firstbitline, and to inhibit the unselected memory cell in the first row fromthe programming by applying the inhibit voltage to the second bitline.18. The method of 11, further comprising: coupling second ends of thesource-drain paths of the memory cells in the first and second columnsto a floating voltage.
 19. A memory array, comprising: a plurality ofmemory cells arranged in rows and columns, wherein each memory cellincludes a non-volatile memory (NVM) transistor, wherein memory cells ina same row share a global wordline, and wherein first ends of memorycells in a same column are coupled to a same bitline, and second ends ofthe memory cells in the same column are configured to be coupled to afloating voltage, wherein during programming of a first memory cellassociated with a first row and a first column, a positive voltage isapplied to a first global wordline associated with the first row and anegative voltage is applied to a first bit line associated with thefirst column to apply a first bias voltage to a NVM transistor in thefirst memory cell, while a negative marginal voltage, which has amagnitude less than the negative voltage, is applied to a second globalwordline associated with an unselected second row for programming, andan inhibited voltage is applied to a second bitline associated with anunselected second column for programming to minimize a second biasvoltage applied to memory cells in the unselected second row and columnfor programming.
 20. The memory array of claim 19, wherein the memorycells in the same column are coupled to a same source line, and whereinmemory cells in adjacent columns do not share the same source line.